For increasing the contact safety of electromagnetic relays, it is known, from German Patent No. 3,224,013, to provide the contact spring with a longitudinal slot to form two flexible ends and to equip each end with a contact piece which cooperates with a corresponding counter contact piece on a common fixed contact. The probability of both contact couples to fail due to contamination by minute glass fibers, molding burs, or the like is substantially smaller than with single contacts.
These "twin" contact springs, which are similarly known from German Published Application No. 1,175,807, German Utility Model No. 9,404,775, and German Patent No. 972,072, however, suffer from the difficulty that the spring arms formed by the longitudinal slot are more prone to breakage than the undivided spring. In such a case, while the relay per se is still operative, the broken spring arm may cause unpredictable short-circuits. A further problem of known twin contact springs resides in the fact that the individual spring arms are much softer than the undivided spring so that, when one contact becomes welded, the corresponding spring arm is not stiff enough to retain the actuator in the closed contact position. These properties prevent the use of known twin contact springs in safety relays.
German Patent No. 3,224,468 discloses a contact arrangement in which the contact spring carries two contact pieces each cooperating with a separate fixed contact. In addition to the fact that the total contact resistance of such bridge contacts is twice that of an individual contact couple, the known arrangement increases the safety in contact opening rather than in contact closure.
Further known are so-called "crown" contacts in which at least one of two cooperating contact rivets has a raised peripheral portion which, if the two rivets are somewhat offset with respect to each other, form two contact locations. In addition to the fact that these contact locations have very small areas, the raised periphery is relatively quickly worn in use so that the intended double contact feature is rapidly lost.